(PERL predefined variable) $<digit> Contains the subpattern from the corresponding set of parentheses in the last pattern matched.

(PERL predefined variable) $MATCH The string matched by the last successful pattern match.

(PERL predefined variable) $PREMATCH The string preceding whatever was matched by the last successful pattern match.

(PERL predefined variable) $POSTMATCH The string following whatever was matched by the last successful pattern match.

(PERL predefined variable) $LAST_PAREN_MATCH The last bracket matched by the last search pattern.

(PERL predefined variable) $MULTILINE_MATCHING Set to 1 to do multi-line matching within a string, 0 to tell Perl that it can assume that strings contain a single line, for the purpose of optimizing pattern matches. Default is 0. Use of ``$*'' is deprecated in modern perls.

(Perl builtin function) grep BLOCK LIST This is similar in spirit to, but not the same as, grep(1) and its relatives.

(Perl builtin function) index STR,SUBSTR,POSITION Returns the position of the first occurrence of SUBSTR in STR at or after POSITION.

(Perl builtin function) study SCALAR Takes extra time to study SCALAR ($_ if unspecified) in anticipation of doing many pattern matches on the string before it is next modified.

Sort::PolySort - Tokenizes and sorts a list of strings. You can specify how each string should be tokenized, and what the comparison function should be. [Perl]{oss}

At CPAN

Sort::Versions - Sorts version numbers, which isn't as easy as it sounds. Consider 1.1a [Perl]{oss}

At CPAN

String::Approx - Approximate ("fuzzy") matching for strings. You give it a string, it returns a list of all strings that are n insertions, deletions, or substitutions distant from your string. Fuzzy substitutions are also possible. [Perl]{oss}

At CPAN

Search::Text - A common search interface to a number of different text-based search engines. [Perl]{oss}